The ability to adapt to osmotic stress is an essential process in all livingorganisms. Osmotic adaptation involves a mechanism that is phylogenetically conserved: the accumulation of intracellular osmolytes to prevent the loss of cellular water. These adaptive responses are also of key importance in renal physiology in higher organisms, including man. For example, medullary cells of the vertebrate kidney adapt to interstitial NaCI and urea concentrations that increase greatly and vary widely during normal cyclesof antidiuresis. The longterm objective of this research is to examine the physiology of osmotic adaptation in the eukaryotic yeast Saccharomyces cerevisisae to develop a microbial model of renal cell function. Data accumulated here and elsewhere have shown that cellular responses observed in yeast resemble those seen in renal cells. The three specific aims of this research are: 1) To further examine the role played by quaternary ammonium compounds (QACs) in the adaptive responses of yeast. Yeast and heterologous QAC transporters will be expressed in yeast. Transport of QACs will be confirmed by radiochemical transport assays. The phenotypic and physiological effects of QAC accumulation or will be examined in vivo; 2) To investigate the mechanism by which phosphorylated inositol (Ins-P) second messengers regulate the expression of genes during osmotic stress. Genome array analysis will initially be used to identify genes that are PLC1 dependent. URA3 and lacZ fusions to those genes will then permit identification of mutations that cause defects inthe Ins-P pathway; 3) To determine the physiological role played by hydrophilic proteins in maintaining viability during osmotic stress. Genes for hydrophilic proteins will be deleted. The effects of these deletions on the loss of viability over time will be examined in vivo. SFSU is an ethnically diverse campus that serves a substantial minority population. Both undergraduate and graduate students will be recruited from this population and trained in microbial physiology and molecular technique sused to pursue the objectives posed above. Students will participate in the formulation of hypotheses, design experiments and analyze data analysis that will enable them to successfully pursue further training or careers in the biomedical sciences.